Hi,

I am upgrading the buffer spring in my 5.56 AR to a more robust spring along with the buffer.  There are no HD buffers for 9mm AR's (that I know of).

Can I also upgrade the buffer spring in my 9mm AR with the upgraded 5.56 buffer spring?

I know size wise it should work, but how about in reality?

Thanks for your help.

The standard 9mm buffers are heavier than standard CAR buffers because the 9mm works on a blowback principle of retarding rearward motion of the bolt until chamber/barrel pressure is down.  If you get too heavy a buffer or spring then you may have function issues.

In the direct gas impingement system of a 5.56 the heavier buffer can increase reliability a bit in short gas system carbines because they also retard rearward motion and bolt unlocking until chamber pressure (much greater in a rifle cartridge) drops so that the extractor isn't trying to pull a fully expanded cartridge case out of the chamber while it is at peak pressure.

Generally with a 9mm there isn't a lot of reserve power there, and the spring/buffer combos are chosen to give teh best relaibility with the widest variety of ammo.

The part numbers for Colt's .223 and 9mm carbine buffer spring are the same.